1. Technical Field
The present disclosure relates to safety helmet design and more specifically to reducing kinetic energy transmission after various types of impacts by utilizing foam structures having graded properties.
2. Introduction
In the United States, hundreds of thousands of people each year are involved in athletic, cycling or motorcycle accidents resulting in head injury. Much of the subsequent damage is caused by the transmission of kinetic energy to the brain, as well as shear forces. Although existing bicycle helmets reduce deaths and brain injuries, current designs focus more on aesthetics and aerodynamic performance than safety, in part due to market demands. In addition, the helmet industry is essentially self-regulating and therefore not likely to make significant improvements to helmets unless the improvements prove to be cost-effective and/or markedly more effective. Advances in polymeric materials provide novel approaches to helmet design and construction. Significant improvements in viscoelastic (active) dampening, low loss elastomers, and gradient rigidity materials have already given rise to enhanced athletic equipment and protective gear.
Crashes and impacts to the head in sports often result in head trauma due to the rigid construction of helmets. The severe consequences of concussive brain injuries have become increasingly recognized in many sports, particularly recently in professional football and ice hockey. It has also long been recognized that boxers often suffer significant cognitive decline, even in non-professional contests where protective head gear is required. Professional and college sports teams would likely switch to a new type of helmet, if such a design were clearly shown to reduce post-traumatic brain injury.
In addition to athletics, improved helmet designs have applications in the military. Brain injury is the leading cause of disability for military personnel deployed in Iraq and Afghanistan. Although military helmet designs have improved in recent years, they are intended primarily to prevent missile/shrapnel penetration, and do little to reduce the energy transmitted to the brain, which is a major contributor to subsequent disability. The mechanisms of traumatic brain injury due to blast forces remain unclear, but brain injuries related to explosives are by far the most common cause of death and disability in Iraq and Afghanistan. Experimental evidence indicates that the use of advanced body armor may contribute to the increase in brain injuries, both by protecting against death from injury to major non-brain organs such as the lung, and possibly by transmitting kinetic energy through larger blood vessels to the brain.
Existing helmet designs do not adequately address the critical problem: kinetic energy from the impact is transmitted to the brain through primary, secondary and tertiary mechanisms—resulting in concussion, brain damage and even death.